The present invention relates to an apparatus and method for providing a homogeneous suspension of an agent in a suspending medium.
A suspension is a mixture of fine, non-settling particles of any solid within a liquid or gas suspending medium. The particles are referred to as the dispersed phase, and the suspending medium is referred to as the continuous phase. The fine particles tend to persist in a suspended state go long as dissipative forces that encourage accumulation are overcome or compensated for. When the compensation becomes inadequate due to, for example, buoyancy, gravity acting on agglomerated macroparticles, or the nonconservative forces of fluid viscosity, particle motion is no longer energetic enough to resist the acting forces within a stationary container, and the particles will accumulate in various forms, such as agglomerates, clumps, sediments, and the like. Once particles accumulate in one of these forms, they must be resuspended within the suspending medium by agitation.
One example of a suspension is a biomedical contrast imaging agent. Contrast agents may contain particles suspended in a pharmaceutically acceptable liquid suspending carrier medium. When injected into the vascular system of a patient, the contrast agent is transported in the bloodstream from the injection site to reach the targeted tissue or organ to be imaged. The agent provides contrast at the target site for enhancement of the resulting image. Imaging techniques used for medical diagnosis and therapy frequently rely upon contrast agents to enhance the quality of the images acquired.
The image enhancement value of a contrast agent is improved if the contrast agent is delivered to a patient at a controlled rate to produce an optimum concentration in the targeted tissue or organ for the specific imaging period. The dose must be sufficient to maintain a concentration of contrast agent in the targeted tissue or organ within the effective range for the minimum period to complete the imaging procedure. These parameters require accurate and precise dosing. Frequently, excess contrast agent is administered to ensure an adequate concentration at the target site.
Contrast agents may be administered relatively rapidly and over a relatively short period of time as a bolus injection, or over a relatively longer period of time and at a slower rate as an infusion. There are several advantages of infusion of contrast agent versus a bolus injection: perfusion studies may be performed over an extended time to visualize the flow of blood in an organ or specific tissue, the duration of the diagnostic imaging procedure may be extended, and elevated concentrations of contrast agent in the blood of the targeted tissue are avoided so that the image will not be overly attenuated. The disadvantages of infusion, however, are that the patient is receiving contrast agent over a longer time period, during which the agent may come out of suspension. This necessitates resuspension of agent during the imaging procedure.
Contrast agents may be administered by infusion using various types of devices. A conventional syringe may be used to inject contrast agent either manually or using an automated injector. A power injector may also be used, where a motor-driven plunger drive slowly and continuously advances the plunger of a syringe to incrementally dispense the syringe contents over an extended time and according to predetermined injection parameters such as flow rate, volume, duration, and time. Power injectors are commonly used for infusions since they provide greater reliability and consistency in infusion rate and dosage when compared to manual injectors.
A primary disadvantage of delivering a contrast agent suspension with a conventional syringe or a conventional power injector, however, is that the contrast agent may not remain homogeneously suspended over the duration of the infusion. As a result, contrast agent dispensed at or near the end of the infusion may have a different composition and/or density, compared with the contrast agent dispensed at or near the beginning of the infusion. The resulting image may contain artifacts due to non-uniform delivery of agent, which may result in misleading or inaccurate images. If the image quality is not suitable for its intended purpose, the entire imaging procedure may have to be repeated with additional cost, patient inconvenience, patient risk, and unnecessary utilization of facility resources.
One solution to this problem is to continuously agitate the contrast agent dispensed using a power injector. This may be accomplished by placing an agitation source, such as a magnetic stir bar, within a syringe barrel containing the suspended contrast agent and activating the stir bar by a coupled magnetic stir plate adjacent to the syringe. Another solution is to interrupt the injection, remove the syringe from the power injector, and manually agitate the contents. Yet another solution is to modify a conventional power injector to allow planetary revolution of the syringe about a longitudinal axis during injection.
These solutions are less than satisfactory. Such devices may be bulky and/or intricate, and may be difficult to use and accommodate in an area where imaging is to be performed. A modified power injector may not comply with existing syringe standards, requiring the use of customized, non-standard syringes. The discontinuity in delivering contrast agent may also adversely impact the quality of the imaging procedure by delaying a critical infusion time. Furthermore, the attendant must monitor the contrast agent within the syringe barrel for detecting non-suspended contrast agent, and must then intervene to resuspend the sedimented agent. Manual manipulation to resuspend the contrast agent has the potential for contamination and/or human error, and may delay a critical point of the procedure, or even the entire procedure. The use of a magnetic stirrer introduces an additional component that must be sterilized and introduced into the syringe barrel, and requires a magnetic stir plate. A modification to a conventional power injector necessitates additional hardware, introduces an additional level of mechanical complexity, consumes space, and may not adhere to current syringe size standards.
Thus, an apparatus that is convenient to use, maintain, and store, and that results in maintenance and injection of an agent suspended within a suspending medium for at least the duration of an infusion procedure, and a method of using such an apparatus, is needed.
The present invention provides these and other features. The invention is directed to apparatus and methods for suspending an agent in a suspending medium within a container, rotating the container to maintain the suspension for extended periods, and selectively delivering the agent while suspended from the container. Further, the present invention provides apparatus and methods that permit the providing of agent to be paused or interrupted while continuing to maintain the suspension of the agent. An example of such a suspended agent is a contrast agent suspended in a suspending medium of a pharmaceutically-acceptable liquid.
An embodiment of the apparatus includes a rotary drive assembly operably connected to a container and an actuator drive assembly operably coupling the rotary drive assembly to an actuator of the container. The rotary drive assembly rotates the container about an axis of the rotary drive assembly so that the agent achieves and maintains a suspended state within the container. The actuator drive assembly transfers a force from the rotary drive assembly to the actuator of the container for operating the actuator to provide the agent in a suspended state from the container.
In one embodiment, the rotary drive assembly has a holder for the container coupled the container, and a motor that rotates the holder about the axis of the rotary drive assembly. As the motor rotates the holder, the container rotates in a planetary fashion about the axis. The holder may extend radially outward from the container so that the rotation is a planetary rotation. In one aspect, the rotary drive may include a threaded spindle with a first portion that is operably connected to the motor for rotation, and a second portion that is connected to the holder. The actuator drive assembly may include a coupling member for operating the actuator of the container, and may also include a clutch assembly that can releasably engage the coupling member with the spindle. For dispensing the suspended agent, a connector, such as a catheter, may be provided between the container and a patient. The apparatus may further include a switch to halt the actuating and rotary drive assemblies.
An alternative embodiment of the apparatus has a housing that encloses the container, an inner member that hold the container, and a motor oprerably coupled with the inner member for rotation of the inner member. The motor rotates the inner member relative to an axis of the housing to maintain the agent in suspension within the suspending medium. The rotation of the inner member also operates the actuator of the container for providing agent in suspension from the container.
An embodiment of the method comprises rotating the container about an axis of rotation sufficient to suspend the agent and delivering the agent from the container by exerting a force upon the actuator sufficient to operate the actuator as the container is rotating to maintain the agent in suspension. The rotating and the delivering may occur simultaneously or the rotating may occur before the delivering. Alternatively, the delivering may be interrupted while maintaining the rotating. In certain embodiments, the container may be rotated in a planetary orbit about the axis of rotation. In other embodiments, the container axis and the axis of rotation are collinear. The container may be prefilled with the agent, such as a contrast agent.
The design of the present invention is lighter, smaller, and relatively inexpensive to manufacture and use, compared with other alternatives such as a dedicated infusion pump that has been modified to achieve adequate mixing. In contrast to a modified power injector, the present invention can accommodate syringes of standard sizes.
Thus, the apparatus and method provide and maintain a homogeneous suspension of an agent, such as a contrast agent, in a suspending medium. This is valuable for extending the duration over which the contrast agent may be efficaciously injected for imaging enhancement. The apparatus is mechanically simple for reliable operation with infrequent maintenance, resulting in minimal non-operational time or downtime, and is compact for flexible positioning in a procedure room. These and other objectives, advantages, features, and embodiments will be apparent with reference to the following drawings and detailed description.